1. Field of the Invention
The present invention relates to a wireless communication technique for optimizing transmission/reception conditions in transmitting/receiving a wireless signal.
2. Description of the Related Art
In recent years, along with popularization of devices equipped with a wireless communication function, wireless communication is increasingly used in communication between the devices. For example, consumer devices such as a home theater are also equipped with a wireless communication function.
Along with this, data used in wireless communication include not only conventional computer data but also video and audio stream data.
In general, the amount of stream data is larger than that of conventional computer data. For this reason, a wireless communication device which processes stream data needs to execute processing for reducing transmission delay fluctuations in communication. In the case of a wireless communication device included in, e.g., a home theater, one control station such as a DVD player transmits stream data to a plurality of terminal stations such as loudspeakers. The control station, therefore, needs to broadcast the data.
Various communication methods for the wireless communication devices have been proposed.
As an example, a communication method using redundant multiplexing is available. In the method, identical stream data are multiplexed by frequency multiplexing, code multiplexing, or polarization multiplexing, multiplexed data is transmitted via a redundant communication path, and the receiving side selects a path whose reception state is good, thereby improving connection quality.
There has been proposed a communication method in which the transmitting side transmits data to a number of receiving sides via a wide directional antenna, and each of the receiving sides points a beam toward the transmission side using its narrow directional antenna, thereby improving a wireless signal strength between the transmitting side and the receiving side, and achieving a high communication rate.
Furthermore, there has been proposed a communication method which combines those communication methods (the communication method using redundant multiplexing and that using directional antennas).
In the communication method which combines the communication method using redundant multiplexing and that using directional antennas, it is necessary to set a plurality of parameters, i.e., a multiplexing scheme between the transmitting side and the receiving side and the beam direction on the receiving side.
Such communication method needs to execute “training processing” for determining, through training, optimum transmission/reception conditions such as an optimum multiplexing scheme and an optimum beam direction.
As the switching method of the communication scheme using redundant multiplexing, the following method has been devised. That is, identical codes are alternately time-divisionally transmitted with horizontal polarization and vertical polarization, and when detecting a decrease in reception power, the receiving side switches the polarization type to the other (see, e.g., Japanese Patent Laid-Open No. 64-060118).
Furthermore, as a method of detecting an optimum polarization type on the transmitting and receiving sides, the following method has been devised. That is, a polarization plane angle on the transmitting side is rotated, and an optimum state is detected by closed-loop control or open-loop control on the receiving side (see, e.g., Japanese Patent Laid-Open No. 2003-520545).
On the other hand, as a method of detecting an optimum beam direction of a reception antenna, the following method has been devised. That is, a beam is pointed toward the transmitting side by scanning all beam directions and determining a radio wave arrival direction (see, e.g., Japanese Patent Laid-Open No. 2005-045384).
If, however, the training processing is executed using a conventional method, the receiving side must determine reception conditions by sequentially switching settable multiplexing schemes and polarization types after detecting a transmission signal and synchronizing transmission and reception paths.
For this reason, in a wireless communication system based on the premise that there exist a control station and a plurality of terminal stations and the control station broadcasts data, it takes time to complete the training processing. This is because in such wireless communication system, all transmission and reception communication paths must be synchronized, and after that, pairs of multiplexing schemes and pairs of beam directions must be sequentially switched and measured while synchronizing the transmission and reception paths.
In addition, if a plurality of control stations are provided to improve the reliability of wireless communication, the training processing must be executed a number of times equal to the number of control stations, thereby prolonging the training processing time.